1. Field of the Invention
The present invention relates to a flat circular waveguide device suitable for use as a broadcasting antenna or the like.
2. Description of the Prior Art
A variety of flat circular waveguide devices have heretofore been proposed, including those having a coaxial cable, such as shown and indicated generally at "a" in FIG. 1. and those having a waveguide tube, such as shown and indicated generally at "b" in FIG. 2.
Incidentally, FIGS. 1 and 2 illustrate also the inner conductor c1 of a coaxial cable c, the outer conductor c2 of the same coaxial cable c, a waveguide tube d, an upper wall f formed of a metallic plate having slots g, a lower wall h formed of a metallic plate, a terminal resistor i, and a feeding opening j.
Either one of those conventional flat circular waveguide devices, however, has drawbacks that the feeding parts, such as the coaxial cable c and the waveguide tube d, do not match the wave-guiding space e, and thereby power is reflected by the junction of the coaxial cable c or the waveguide tube d, and the wave-guiding space e. Consequently, the power fed to the flat circular waveguide device cannot be radiated effectively.
A flat circular waveguide device as shown in FIGS. 3 and 4 is considered to enhance antenna gain and to enable the use of a small universal terminal resistor, by concentrating the power fed thereto in the central portion of the wave-guiding space so that the power is radiated uniformly through the power radiating opening. This flat circular waveguide device has, as shown in FIGS. 3 and 4, a pair of metallic plates b' and c', one of which having power-radiating slots a', disposed separately from and oppositely to each other, a metallic peripheral wall d' interconnecting the respective peripheries of those metallic plates b' and c' and defining, together with the metallic plates b' and c', an internal wave-guiding space e', and an intermediate metallic plate g' disposed within the wave-guiding space e' so as to form a by-pass gap f' between the periphery thereof and the metallic peripheral wall d', and is adapted to concentrate the power fed thereto from the peripheral wall d' doward the central portion of the wave-guiding space e' as indicated by an arrow Pf.
In FIGS. 3 and 4, also shown are a coaxial cable h', the outer conductor h1' of the coaxial cable, the inner conductor h2' of the coaxial cable, a terminal resistor i', and a conductive matching plate j'.
The flat circular waveguide device shown in FIGS. 3 and 4, however, has a drawback that the power fed thereto is reflected in the corner park k' of the wave-guiding space e' including the by-pass gap f' causing great difference between the upper wave-guiding compartment and the lower wave-guiding compartment in inner field, as shown in FIG. 5, and thereby the power supplied thereto cannot be radiated effectively through the corner part k'.
This flat circular waveguide device has a further drawback that the side lobe increases to deteriorate the antenna efficiency, because slots (or slits) a', i.e., power radiating openings, are arranged at an interval corresponding to the line wavelength .lambda. to radiate power of the same phase through the slots.